A small portion of the radio frequency (RF) spectrum is assigned to each communications carrier. The assigned spectrum, therefore, must be used efficiently in order to allow the maximum number of frequency users to have access to this spectrum. Multiple access modulation techniques have been developed to provide optimum utilization of the RF spectrum. Examples of such modulation techniques include time division multiple access (TDMA), frequency division multiple access (FDMA), and code division multiple access (CDMA).
There is a wide variance in the performance of wireless networks. A conventional wireless cellular network covers a relatively large geographical area, but provides a relatively low bandwidth. Such wireless networks use regulated portions of the radio spectrum and are shared by many users. The infrastructure costs of wireless networks are relatively high due to the size and complexity of the cellular network equipment.
Other wireless networks, such as CDMA2000-EV-DO/DV networks, offer higher bandwidth and enhanced data services, such as web browsing. However, these networks also pack many users into a relatively small portion of the regulated spectrum. Other types of radio networks are adapted to improve spectral efficiency with increased speed and smaller coverage areas. For example, an IEEE 802.11x (or Wi-Fi) network may transmit at speeds up to 11 Mbps using a Direct Sequence Spread Spectrum (DSSS) mode or at speeds up to 54 Mbps using an Orthogonal Frequency Division Multiplexing (OFDM) mode.
An access point conforming to an IEEE 802.11x (e.g., IEEE 802.11b) network may cover an area of a few hundred feet in diameter. Each such access point is connected to a larger network (e.g., Internet). One such example is Wi-Fi VoIP (Wireless Fidelity Voice over Internet Protocol), through which a mobile device user can place a wireless telephone call over the Internet, using the technology specified in IEEE 802.11b at the network access point. VoIP is a method for taking analog audio signals and converting them into digital data that can be transmitted over the Internet. Conventional VoIP telephone communications are enabled by VoIP network carriers, which utilize VoIP networks, e.g. the Internet, to place VoIP based telephone calls. VoIP enabled and compatible networks include VoIP switching for proper routing and billing of VoIP based telephone calls.
In order to cover larger geographical areas, a relatively large number of IEEE 802.11x network access points and relatively large wire-line back haul networks are required. In part, due to the relatively small geographical coverage area of each network access point, the resulting IEEE 802.11x based network may thus be prohibitively expensive to set up. Further, the small coverage areas may lead to many “dead zones” in which mobile device users are unable to place telephone calls using the VoIP network.